Method and apparatus for casting printing plates



J 1956 B. R. PRESTON ET AL 2,748,433

METHOD AND APPARATUS FOR CASTING PRINTING PLATES Filed Sept. 25, 1952/-\\R PRESSURE- METHGD AND APPARATUS FOR CASTING PRINTING PLATES.

Benjamin R. Preston and Donald A. Richmond, Kalamazoo, Mich.

Application September 25, 1952, Serial No. 311,486

3 Claims. (Cl..22,-58)

This invention relates to improvement in method and apparatus forcasting printing plates.

The principal objects of this inventionv are:

First, to provide plate casting apparatusthat will rapidly produceprinting plates of sound character and particularly without voids andsoft spots.

Second, to provide plate casting apparatus that will maintain thebacking metalof the plate under hydrostatic pressure head until theentire usable portion of the plate is. solidified.

Third, to' provide plate casting apparatus in which the backing metalcools through the shell at the face of the plate and solidifiesprogressively rearwardly from the shell and upwardly from the bottomthereof.

Fourth, to provide plate casting apparatus with means for rapidly anduniformly heating and cooling the mold chamber.

Fifth, to provide a method of casting printing plates in which themolten backing metal which is cast behind the shell solidifiesprogressively rearwardly from the shell and upwardly from the bottom ofthe plate so that the metal is at all times under hydrostatic pressure.as it solidifies assuringuniformly solid' plates.

Sixth, to provide a method of casting printing plates which includes, anovel method of heating. and cooling the mold chamber to obtain uniformdesirable temperatures therein.

Seventh, to providea methodofheatingthe mold chamber of a plate castingmold which will" bring the chamber and a shell therein to a uniformtemperature proper for annealing the shell prior to castingbacking metaltherebehind.

Eighth, to provide method and apparatus for casting.

printing plates which will provide plates of uniform high.

quality in a minimum of time.

Other objects and advantages of the invention will be; apparent from aconsideration of" the following, description and claims. The drawings ofwhich there is one sheet illustrate anapparatus embodyingthe inventionand with which the method may be carried out.

Fig. 1 is a side elevations-1' view partially broken away in crosssection of a plate casting mold and of" heating and cooling apparatusassociated-with the mold, the heating and coolingapparatus beingillustratedconventionally.

Fig. 2. is a longitudinally cross sectional view through the mold takenalong the plane ofthe line 2-2 in Fig. 3'.

Fig. 3 is a transverse cross sectional View through the mold taken alongthe plane ofth'e line 3- -3 in Fig. 1.

Fig. 1 somewhat conventionally illustrates a plate casting mold 1ti-ltably SUPPOITLCCLOIITBJ suitablebasel'. The

mold includes abed 3 havingpintles 4 projecting from op-J posite sidesthereof intermediate of its-ends; Thmpintles i are rotatably supportedin suitable; bearings int-the base;

Fatented June 5, 1956 so that the bed may be tilted from the horizontalposition illustrated in full lines in Fig. 1 to the vertical positionindicated in dotted lines. Power means for tilting the bed such as thehydraulic cylinder 5 may be provided.

The bed 3 is chambered as at 6 with the upper and inner wall of thechamber forming the casting face 7 of the mold box. The interior of thechamber in the bed is provided with transversely extending ribs 8 whichprovide a circuitous path through the chamber.

One side of the bed 3 is provided with a longitudinal wall 9 extendingfrom the lower end of the bed to the pintle and the extension and pintleco-act to form an outlet passage 10 communicating with the top of thechamber 6 through a port 11. The opposite side and end of the bedcarries a longitudinal wall 12 that provides an inlet passage 13 openingbetween a port in the lower end of the chamber and a passage drilledthrough the opposite pintle. Running seals, one of which is illustrated.at 14 provide fluid connections to the passages 10 and 13.

Hinged to the bottom of the bed as at 15 is a cover 16 adapted to beclosed over the casting face 7 of the bed. Means are provided forclamping the cover to the bed and in the present instance clamp bolts 17and nuts 18 conventionally illustrate this means. In casting type platesbearer strips 19 are positioned along the sides and bottom of the bedand clamped thereagainst by the. cover as is common in plate castingapparatus.

Associated with the mold 1 are a heater 2! and cooler 21 for a heattransfer fluid. A hot fluid pump 22 is connected to deliver from aconduit. 23, expansion tank 24, conduit 25, one of the running seals14-, and the passage 12 to the bottom of the mold chamber to deliverfluid to the bottom of the heater. A cold fluid pump 26 is connected todeliver from the cooler 21 to a conduit 27, expansion tank 23, a branchof the conduit 25, and the. bottom of the chamber in the mold bed. Afluid conduit 2? is connected to the other running seal to communicatebetween the. top of the, chamber in themold. bed and a. two way valve30. Thevalve 30 isconnected to direct fluid alternatively to the,conduit 31 and the cooler or from the conduit 32 and the heater.

The expansion tank 28' is desirably connected to a source of airpressure as at 33 to maintain the system under pressure. A thermometerindicated at 34 indicates the temperature of the fluid being returnedfrom the chamber in the mold bed while a second thermometer has its bulbor heat responsive element 35 positioned to indicate the temperature ofthe mold bed. The heat transfer system formed by the mold: bed chamber,cooler, heater and conduits is filled with a liquid that desirably hasthe property of having a. high heat holding capacity and of remainingliquid when subjected to high temperature. One desirable type ofliquidis a eutectic mixture of diphcnyl and diphenyloxide. Such a liquidwill keep its liquid character when heated as, high as 500. By providing20 pounds air pressure on the expansion. tank 28 this liquid can beheated as high as.700 to 750 Without vaporizing.

In casting a printing plate in the mold 1 the electrotype shell 36 isplaced onthe casting face 7. Desirably the shell is tinned as in commonpractice and it is further desirable that the shell shall be furtherannealed. The bearer strips 19 are placed around the shell and siliconerubber sealing strips 37 are placed over the bottom and side edges ofthe shell inwardly of the bearer strips. The cover 16. is. then closedand clamped upon the bearer strips; and sealing strips to hold the shellin place. This leaves a casting cavity 38 behind the shell which cavityis open at the top when the mold is elevated or tilted at verticalposition. Prior to closing and clamping the cover 16 an insulating panelsuch as press board is placed across the face of the cover as at 39. Itis pointed out that the casing cavity is substantially longer than theshell and that the shell is positioned along the bottom of the cavityleaving a cavity extension 40 extending substantially abovethe upper endof the shell. A paper shield 41 is placed over the upper edge of theshell and extended out the top of the cavity. The shield is held to theshell by being pasted thereto or by corks 42 clamped in place by thecover.

After the mold has been clamped and elevated the pump 22 is started andthe valve is turned to receive liquid through the conduit 32 from theheater. The heater is operated to deliver hot liquid to the chamber inthe mold bed and to heat the bed and the shell. The heat transfer liquidmay be heated up to the burning temperature of the metal of the shell,which is approximately 700, but lower temperatures between 400 and 500also produce highly satisfactory results. The higher temperature of thebed'and shell anneal the shell and the tin coating thereon but withpreannealed shells this high temperature is unnecessary. After the moldand shell have reached the desired temperature as indicated by thethermometers 34 and 35 the molten backing metal is delivered into thecasting cavity fom a spout 43.

Immediately after the casting cavity is filled with molten backing metalthe valve 30 is turned to direct liquid from the bottom of the mold bodychamber to the cooler 21 and the pump 26 is started. The pump 22 isstopped. Depending upon the capacity of the cooler 21, the mold body andthe newly cast plate can be cooled rapidly. The heat of the moltenbacking metal is sufficient to fuse the tin coating on the shell tosecurely bond the backing metal to the shell. The temperaturedifferential between the hot backing metal and the cooling liquid shouldnot be so great as to subject the shell to thermal shock but thetemperature difierential should be great enough to rapidly carry thebacking metal through its 4 to 5 solidifying range. Desirably thebacking metal is cast at between 600 to 650 and the plate is then cooledto below 570 at which temperature the backing metal solidifies. Asatisfactory cycle is to heat the box and shell to 500 by liquid at 520cast the molten metal at 650 and cool the new plate to 200 by liquid at150. Note that the heat transfer liquid does not need to immediatelyreach the temperature limits stated. For example, 500 liquid will cool650 metal and both the liquid and metal will fall in temperature as thecooling progresses.

It is pointed out that the hot liquid for heating the mold is still at atemperature lower than the temperature of burning gases which have beenused heretofore to heat similar molds. The entire mold and shell aretherefore brought to a uniform temperature that is suflicient forcasting without danger of burning the shell. The cooling liquid beingdirected upwardly through the body chamber cools the plate first throughthe bottom portion of the shell and progressively upward and rearwardfrom the shell. The line of solidification of the backing metal at onepoint in its cooling stage is indicated at 44 in Fig. 2.

Thus the partly solidified portions of the backing metal are at alltimes subjected to the hydrostatic pressure of the still molten metalabove and behind the line of solidification. This means that all bubblesor voids in the metal will be forced to the rear and top of the platewhere they can be easily removed by sawing off the top of the elongatedcast plate or by planning a thin layer from the book of the plate.

Having thus described our invention, what we claim as new and desire tosecure by Letters Patent is:

1. Type plate casting apparatus comprising, a mold box bed adapted toreceive a type shell, a cover closable over said bed, said bed having aforced-cooling chamber formed therein co-extensive with the shellreceiving area thereof, a sheet of heat insulating material disposedover the face of said cover to oppose said bed, said cover being ofsolid material and exposed to the air on its outer side, a support forsaid bed and cover adapted to hold the same in alternate horizontal andvertical positions, bearer strips adapted to be positioned between saidbed and cover along the bottom and sides thereof relative to thevertical position of the bed, a fluid heater, a fluid cooler, a pair ofpumps connected to circulate fluid through said cooler and heater, afluid conduit and a two way valve connecting the output side of saidheater and the input side of said cooler to the upper portion of saidchamber, a second conduit connected to the lower end of said chamber andhaving branches connected to said pumps and said heater and cooler, athermometer positioned to indicate temperature changes in said chamber,a recirculating system being formed by said conduits, heater, cooler andchamber, an expansion tank in one of said conduits, a source of airpressure exceeding 15 pounds per square inch opening to said tank, and abody of fluid in said heater, chamber and cooler characterized by theproperty of remaining liquid in the temperature range of to 500 F.

2. Type plate casting apparatus comprising, a mold box bed adapted toreceive a type shell, a cover closable in spaced relationship over saidbed, said bed having a forced cooling chamber formed thereinco-extensive with the shell receiving area thereof, a sheet of heatinsulating material disposed over the face of said cover to oppose saidbed, said cover being uncooled except by natural radiation from itsexposed surfaces, a support for said bed and cover adapted to hold thesame in alternate horizontal and vertical positions, means adapted toclose the space between said bed and cover along the bottom and sidesthereof relative to the vertical position of the bed, a fluid heater, afluid cooler, means connected to circulate fluid separately through saidcooler and heater, a fluid conduit connecting the output side of saidheater and the input side of said cooler to the upper portion of saidchamber, a second conduit connected to the lower end of said chamber andhaving branches connected to said heater and cooler, a two way valveassociated with one of said conduits to selectively direct fluid fromsaid heater and said cooler to said chamber, a thermometer positioned toindicate temperature changes in said chamber, a recirculating systembeing formed by said conduits, heater, cooler and chamber, an expansiontank in one of said conduits, a source of air pressure exceeding 15pounds per square inch opening to said tank, and a body of fluid in saidsystem characterized by the property of remaining liquid at atmosphericpressure in the temperature range of 80 F. to 500 F.

3. Type plate casting apparatus comprising, a mold box bed adapted toreceive a type shell, a cover closable in spaced relationship over saidbed, said bed having a forced cooling chamber formed thereinsubstantially covering the shell receiving area thereof, a heatinsulating surface on the face of said cover opposed to said bed, saidcover being uncooled except by natural radiation from its exposedsurfaces, a support for said bed and cover adapted to hold the same inalternate horizontal and vertical positions, means adapted to close thespace between said bed and cover along the bottom and sides thereofrelative to the vertical position of the bed, a fluid heater, a fluidcooler, a fluid conduit connecting the output side of said heater andthe input side of said cooler to the upper portion of said chamber, asecond conduit connected to the lower end of said chamber and havingbranches connected to said heater and cooler, means for circulatingfluid through said chamber, means for selectively directing thecirculated fluid to said cooler and heater, a recirculating system beingformed by said conduits, heater, cooler and chamber, and a body of fluidin said system characterized by the property of remaining liquid atatmospheric pressure in the temperature range of 150 F. to 500 F.

References Cited in the file of this patent UNITED STATES PATENTS 6 HuckNov. 1, 1938 Van Bolt Oct. 24, 1939 Bungay Dec. 5, 1939 Peterson May 25,1948 Miller Jan. 2, 1951 Jung July 28, 1953 FOREIGN PATENTS GreatBritain Jan. 11, 1939

